The magnetic resonance imaging subset of the mngu0 articulatory corpus

This paper announces the availability of the magnetic resonance imaging (MRI) subset of the mngu0 corpus, a collection of articulatory speech data from one speaker containing different modalities. This subset comprises volumetric MRI scans of the speaker's vocal tract during sustained production of vowels and consonants, as well as dynamic mid-sagittal scans of repetitive consonant-vowel (CV) syllable production. For reference, high-quality acoustic recordings of the speech material are also available. The raw data are made freely available for research purposes.     

The influence of short strong hydrogen bonding on the structure and the physicochemical properties of alkyl-N-iminodiacetic acids in solid state and aqueous systems

Alkyl-N-iminodiacetic acids with varying alkyl chain lengths have been prepared and characterized with respect to structure, acidic properties, and ability to form aggregates in water. The alkyl-N-iminodiacetic acids are the group of ligands with the lowest molecule weight which can be characterized as chelating surfactants, compounds with surface chemical properties which at the same time have a high ability to bind metal ions. The solid alkyl-N-iminodiacetic acids have a unique structure with neutral zwitterionic units linked together to polymer chains through a short strong hydrogen bond, d(O(-H)...O) approximately 2.46 A, and where the nu(O-H) stretching vibration at ca. 720 cm(-1) supports the presence of such a hydrogen bond. The polymer chains are cross-linked together to bilayers through relatively strong hydrogen bonds between ammonium and carboxylate groups, and where the parallel alkyl groups are interdigitating each other; the bilayer surface consists of hydrophilic iminodiacetic acid groups. The acidic properties of monomeric alkyl-N-iminodiacetic acids in water are in the expected ranges with pK(a) values of about 1.7, 2.3, and 10.3. n-Octadecyl-N-iminodiacetic acid, present as aggregates in water, displays very acidic properties of the first proton, and a substantially weakened acidity of the second proton, pK(a2) = 5.5-7.5, depending on ionic strength, and pK(a3) = 9.5-10.5. This pattern of the acidic constants strongly indicates that the polymer structure with short strong hydrogen bonds is maintained in the aggregates and that such bonds can exist in aqueous systems if they are supported by a strong and rigid backbone structure, as the bilayers of well-organized long interdigitating alkyl chains in the studied systems. Hydrogenbis(methyl-N-iminodiacetic acid) perchlorate precipitates from perchloric acidic solutions of methyl-N-iminodiacetic acid. The structure is built up of dimers of zwitterionic methyl-N-iminodiacetic acid units linked together by an extra proton in a short strong hydrogen bond, d(O(-H)...O) approximately 2.456(6) A, and nu(O-H) = 789 cm(-1).     

Structure of the hydrated, hydrolysed and solvated zirconium(IV) and hafnium(IV) ions in water and aprotic oxygen donor solvents. A crystallographic, EXAFS spectroscopic and large angle X-ray scattering study

The tetrameric hydrolysis products of zirconium(IV) and hafnium(IV), the zirconyl(IV) and hafnyl(IV) ions, [M(4)(OH)(8)(OH(2))(16)(8+)], often labelled MO(2+).5H(2)O, are in principle the only zirconium(IV) and hafnium(IV) species present in aqueous solution without stabilising ligands and pH larger than zero. These complexes are furthermore kinetically very stable and do not become protonated even after refluxing in concentrated acid for at least a week. The structures of these complexes have been determined in both solid state and aqueous solution by means of crystallography, EXAFS and large angle X-ray scattering (LAXS). Each metal ion in the [M(4)(OH)(8)(OH(2))(16)](8+) complex binds four hydroxide ions in double hydroxo bridges, and four water molecules terminally. The M-O bond distance to the hydroxide ions are markedly shorter, ca. 0.12 A, than to the water molecules. The hydrated zirconium(IV) and hafnium(IV) ions only exist in extremely acidic aqueous solution due to their very strong tendency to hydrolyse. The structure of the hydrated zirconium(IV) and hafnium(IV) ions has been determined in concentrated aqueous perchloric acid by means of EXAFS, with both ions being eight-coordinated, most probably in square antiprismatic fashion, with mean Zr-O and Hf-O bond distances of 2.187(3) and 2.160(12) A, respectively. The dimethyl sulfoxide solvated zirconium(IV) and hafnium(IV) ions are square antiprismatic in both solid state and solution, with mean Zr-O and Hf-O bond distances of 2.193(1) and 2.181(6) A, respectively, in the solid state. Hafnium(IV) chloride does not dissociate in N,N'-dimethylpropyleneurea, dmpu, a solvent with good solvating properties but with a somewhat lower permittivity (epsilon= 36.1) than dimethyl sulfoxide (epsilon= 46.4), and an octahedral HfCl(4)(dmpu)(2) complex is formed.     

Experimental evidence for a variable first coordination shell of the cadmium(II) ion in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution

A combined extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS) investigation has been performed to evaluate the coordination structure of the cadmium(II) ion in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea (dmpu) solutions. This approach has singled out the existence of a flexible coordination shell around the cadmium(II) ion in aqueous and dimethyl sulfoxide solutions, whereas a regular octahedral complex is detected in dmpu. The EXAFS and LAXS techniques provide different values of the Cd-O first shell distance (2.27(1) A and 2.302(5) A, respectively) for the hydrated and dimethyl sulfoxide solvated complexes, and this discrepancy is originated by the simultaneous presence of hexa- and heptacoordinated complexes in solution, giving rise to a broad distribution of distances around the ion. These findings demonstrate that, in solution, the cadmium(II) ion forms quite flexible hydration and dimethyl sulfoxide solvate complexes undergoing a solvent exchange with unusually stable seven-coordinated intermediate complexes, and therefore the mean ion-solvent distance is longer in solution than in the solid state. In the dmpu solution, due to the bulkiness of the solvent molecules, the octahedral cadmium(II) solvate is extremely crowded and it is not possible for a seventh ligand to enter the inner-coordination shell. This investigation shows that the combined analysis of the EXAFS and LAXS data allows a reliable determination of the structural properties of electrolyte solutions, also in the presence of flexible coordination shell with a variable number of coordinating molecules.     

High-resolution 2D 1H-15N NMR characterization of persistent structural alterations of proteins induced by interactions with silica nanoparticles

The binding of protein to solid surfaces often induces changes in the structure, and to investigate these matters we have selected two different protein-nanoparticle systems. The first system concerns the enzyme human carbonic anhydrase II which binds essentially irreversibly to the nanoparticles, and the second system concerns human carbonic anhydrase I which alternate between the adsorbed and free state upon interaction with nanoparticles. Application of the TROSY pulse sequence has allowed high-resolution NMR analysis for both of the protein-nanoparticle systems. For HCAII it was possible to observe spectra of protein when bound to the nanoparticles. The results indicated that HCAII undergoes large rearrangements, forming an ensemble of molten globule-like structures on the surface. The spectra from the HCAI-nanoparticle system are dominated by HCAI molecules in solution. A comparative analysis of variations in intensity from 97 amide resonances in a 1H-15N TROSY spectrum revealed the effects from interaction with nanoparticle on the protein structure at amino acid resolution.     

Dehydroaromatization of quinoxalines: one-step syntheses of trinuclear 1,6,7,12,13,18-hexaazatrinaphthylene titanium complexes

We report the spontaneous coupling of N-heterocycles, initiated by C-H bond activation reactions. The reaction of quinoxalines and the titanocene acetylene complex Cp2Ti{eta2-C2(SiMe3)2}, as an excellent titanocene source, results in the formation of trinuclear 1,6,7,12,13,18-hexaazatrinaphthylene (HATN) titanium complexes. These HATN titanium complexes are thermally stable but sensitive to air and moisture. A three-fold dehydrogenative C-C coupling is proposed as the main step in the presented synthetic procedure. Particularly using commercial starting materials, an efficient route for the dehydrogenative coupling of N-heterocycles, leading to multidentate ligands, has been established.     

Vibrational spectroscopic force field studies of dimethyl sulfoxide and hexakis(dimethyl sulfoxide)scandium(III) iodide, and crystal and solution structure of the hexakis(dimethyl sulfoxide)scandium(III) ion

Hexakis(dimethyl sulfoxide)scandium(III) iodide, [Sc(OS(CH(3))(2))(6)]I(3) contains centrosymmetric hexasolvated scandium(III) ions with an Sc-O bond distance of 2.069(3) angstroms. EXAFS spectra yield a mean Sc-O bond distance of 2.09(1) angstroms for solvated scandium(III) ions in dimethyl sulfoxide solution, consistent with six-coordination. Raman and infrared absorption spectra have been recorded, also of the deuterated compound, and analysed by means of normal coordinate methods, together with spectra of dimethyl sulfoxide. The effects on the vibrational spectra of the weak intermolecular C-H...O interactions and of the dipole-dipole interactions in liquid dimethyl sulfoxide have been evaluated, in particular for the S-O stretching mode. The strong Raman band at 1043.6 cm(-1) and the intense IR absorption at 1062.6 cm(-1) have been assigned as the S-O stretching frequencies of the dominating species in liquid dimethyl sulfoxide, evaluated as centrosymmetric dimers with antiparallel polar S-O groups. The shifts of vibrational frequencies and force constants for coordinated dimethyl sulfoxide ligands in hexasolvated trivalent metal ion complexes are discussed. Hexasolvated scandium(iii) ions are found in dimethyl sulfoxide solution and in [Sc(OSMe(2))(6)]I(3). The iodide ion-dipole attraction shifts the methyl group C-H stretching frequency for (S-)C-H...I(-) more than for the intermolecular (S-)C-H...O interactions in liquid dimethyl sulfoxide.